Capacitive fingerprint sensor with quadrature demodulator and multiphase scanning

A method comprising:

• receiving a pair of differential signals from at least two sensing electrodes of a plurality of sensing electrodes of a fingerprint sensing array disposed along a first axis in response to a drive signal from a pair of drive electrodes disposed substantially orthogonal to and intersecting the at least two sensing electrodes, the received signal derived from the drive signal on the pair of drive electrodes and a mutual capacitance between the drive electrodes and the sensing electrodes;
• modifying the differential signal with at least one phase-shifted reference signal to produce a phase-shifted signal;
• converting the phase-shifted signal to a phase-shifted digital value;
• and
• processing the digital value to produce a result representative of the mutual capacitance between one of the pair of sensing electrodes and one of the pair of drive electrodes.

A fingerprint detection system comprising:

• a plurality of drive (TX) electrodes disposed along a first axis;
• a plurality of receive (RX) electrodes disposed along a second axis, wherein the TX electrodes and the RX electrodes are configured to have a mutual capacitance at each intersection of the TX electrodes and the RX electrodes;
• a drive circuit coupled to the TX electrodes, the drive circuit configured to produce a TX signal on the TX electrodes, wherein at least two TX electrodes are driven by the drive circuit concurrently;
• an analog front end (AFE) coupled to the RX electrodes, the AFE configured to generate a digital value representative of the mutual capacitance, wherein the AFE comprises a quadrature demodulation circuit configured to generate a demodulated signal, and wherein at least two RX electrodes are coupled to the AFE differentially;
• a channel engine configured to generate a capacitance result value based on the at least one digital value;
• a scan control circuit to configure a first multiplexer coupled between the drive circuit and the plurality of TX electrodes and to configure a second multiplexer coupled between the AFE and the plurality of RX electrodes;
• and
• a memory configured to store the capacitance result value generated by the channel engine.